Method and apparatus for manufacturing fin-integrated tube for use in heat exchanger

ABSTRACT

The method of manufacturing a fin-integrated tube for a heat exchanger includes step of disposing a rolling roller group including rolling rollers so as to surround the periphery of a tube, each of the roller crests of the rolling rollers being rounded at an end thereof into an R-shape, widths of the R-shaped ends being gradually increased from one axial end to the other axial end for each of the rolling rollers, and step of causing the roller crests to press the periphery of the tube from the one axial end to the other axial end by axially moving and rotating the rolling roller group relative to the tube so as to deform a part of the periphery of the tube into a spirally projecting portion while shaping it into a spiral fin by gradually squeezing the part of the periphery of the tube using the R-shaped end portions.

This application claims priority to Japanese Patent Application No.2013-18326 filed on Feb. 1, 2013, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus formanufacturing a high temperature-resistant fin-integrated tube for usein a heat-exchanger mountable on a vehicle.

2. Description of Related Art

There are known various heat exchangers which can be used in a coolingsystem, a driving system and an air-conditioning system of a vehicle.FIG. 19 shows a common fin-integrated tube for use in a heat exchanger.This fin-integrated tube includes a tube 200 through whichheat-exchanging medium flows and a plurality of hat-shaped rings 201brazed to the tube 200 such that the tube 200 passes through a stack ofthe hat-shaped rings 201 as fins 202.

It is known to form a plurality of fins integrally with a tube servingas a radiator to provide a compact and highly-efficient heat exchanger.For example, refer to Japanese Patent Application Laid-open No.2001-332666. This patent document describes carving the outer or innerwall of a tube to form a plurality of fins which are integrallyconnected to the tube at their thick proximal end portions. Theplurality of the fins are formed using a carving knife such that theybecome thinner from their proximal end portions to their distal endportions to increase their surface area to thereby increase the heatdissipation effect.

As a heat exchanger mountable on a vehicle, the exhaust heat recoverydevice is receiving attention. The exhaust heat recovery device recoversexhaust heat emitted from an engine. The exhaust heat recovery deviceincludes a fin-integrated tube which contains pure water and is mountedin the exhaust passage of the engine for recovering the exhaust heat.Since this fin-integrated tube is exposed to exhaust gas, it is made ofheat-resistant and corrosion-resistant stainless steel and their finsare joined to the tube using a nickel-based brazing material, forexample.

However, it turned out that the fins of such a fin-integrated tube maybe deformed due to a linear expansion difference in the dissimilar metaljoint by the brazing material in a case of a high-efficiency engine thatemits high-temperature exhaust gas (900° C., for example). Further, ifthe number of the fins is increased to increase the heat exchangeefficiency, manufacturing time and cost increase greatly because thefins have to be joined one by one to the tube.

The inventors of the present invention studied a possibility of adoptionof a fin-integrated tube which does not include any brazing material,and can be manufactured by the method described in the above patentdocument. However, the method of carving the tube surface to form finsas described in the above patent document, which is suitable for thecase where the tube is made of metal easy to carve such as aluminum, isdifficult to use in the case where the tube is made of stainless steel.Further, the wall thickness and the rigidity of the tube have to besufficiently large, while on the other hand, the shapes of the finsformed by carving the outer or inner surface of the tube along its axisand the wall thickness after the carving of the tube are likely to benon-uniform. Hence, it is difficult to reduce individual difference inthe radiation performance. As explained above, it has been difficult sofar to achieve both reducing the manufacturing cost and increasing theheat exchange efficiency.

SUMMARY

An exemplary embodiment provides a method of manufacturing afin-integrated tube for a heat exchanger, the fin-integrated tubeincluding a cylindrical tube and a spiral fin integrally formed in aperiphery of the tube, including the steps of:

disposing a rolling roller group including a plurality of rollingrollers each having a plurality of roller crests on a periphery thereofso as to surround the periphery of the tube with a predetermined leadangle, each of the roller crests being rounded at an end thereof into anR-shape to be an R-shaped end, widths of the R-shaped ends of the rollercrests being gradually increased from one axial end to the other axialend for each of the rolling rollers, so that each of the rolling rollersserves as a gradual roller; and

causing the roller crests of the rolling rollers to press the peripheryof the tube from the one axial end to the other axial end by axiallymoving and rotating the rolling roller group relative to the tube so asto deform a part of the periphery of the tube into a spirally projectingportion while shaping the spirally projecting portion into the spiralfin by gradually squeezing the part of the periphery of the tube usingthe R-shaped end portions of the roller crests of the rolling rollers.

The exemplary embodiment provides also a manufacturing apparatus formanufacturing a fin-integrated tube for a heat exchanger, thefin-integrated tube including a cylindrical tube and a spiral finintegrally formed in a periphery of the tube, including:

a tube holding part for holding a proximal end portion of the tube so asto be rotatable together with the tube; and

a rolling roller head disposed coaxially with the tube so as to beaxially movable relative to the tube;

the rolling roller head having a rolling roller group including aplurality of rolling rollers each having a plurality of roller crests ona periphery thereof, said rolling roller group being configured tosurround the periphery of the tube with a predetermined lead angle,

each of the roller crests being rounded at an end thereof into anR-shape to be an R-shaped end, widths of the R-shaped ends of the rollercrests being gradually increased from one axial end to the other axialend for each of the rolling rollers, so that each of the rolling rollersserves as a gradual roller,

wherein

the rolling roller head is configured to be driven to axially move in adirection from a distal end to a proximal end of the tube and rotaterelative to the tube so as to cause the roller crests of the rollingrollers to press the periphery of the tube in the direction from thedistal end to the proximal end so as to deform a part of the peripheryof the tube into a spirally projecting portion while shaping thespirally projecting portion into the spiral fin by gradually squeezingthe part of the periphery of the tube using the R-shaped end portions ofthe roller crests of the rolling rollers.

According to the exemplary embodiment, there is provided ahigh-performance and low-cost heat exchanger for vehicle use, whichincludes fin-integrate tubes manufactured without use of brazingmaterial.

Other advantages and features of the invention will become apparent fromthe following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a general view of a manufacturing apparatus for manufacturinga fin-integrated tube according to a first embodiment of the invention;

FIG. 2 is a partially enlarged view of the fin-integrated tubemanufactured by a method performed using the manufacturing apparatusaccording to the first embodiment of the invention;

FIG. 3 is a partially enlarged view of a form rolling part of themanufacturing apparatus according to the first embodiment of theinvention;

FIG. 4 is plan and side views of a form rolling roller head constitutingthe rolling part;

FIG. 5 is a partially enlarged view of an exhaust heat recovery deviceincluding the fin-integrated tubes manufactured by the method performedusing the manufacturing apparatus according to the first embodiment ofthe invention;

FIG. 6 is a cross-sectional view of the exhaust heat recovery device;

FIG. 7 is a perspective view of the exhaust heat recovery device;

FIG. 8 is a schematic diagram for explaining a rolling process performedusing the rolling roller head of the rolling part of the manufacturingapparatus according to the first embodiment of the invention;

FIG. 9 is a diagram showing an example of the shapes of the rollercrests of rolling rollers of the rolling roller head;

FIGS. 10 and 11 are schematic diagrams for explaining a fin shapingprocess performed using the rolling rollers;

FIG. 12 is a schematic diagram for explaining variation of effect of therolling rollers depending on variation of the angles of the rollercrests of the rolling rollers;

FIG. 13 is a schematic diagram for explaining variation of the effect ofthe rolling rollers depending on variation of the R-shaped end portionsof the roller crests of the rolling rollers;

FIG. 14 is a schematic diagram for explaining a tube extension at thetime of the rolling process;

FIG. 15 is a cross-sectional view for explaining effects of a extensionabsorbing mechanism of the rolling roller head;

FIG. 16 is a side view showing an example of the shapes of the rollercrests of rolling rollers of a manufacturing apparatus according to asecond embodiment of the invention;

FIG. 17 is a schematic diagram for explaining a tube forming processperformed using the rolling rollers of the manufacturing apparatusaccording to the second embodiment of the invention;

FIG. 18 is a schematic diagram for explaining a method of manufacturinga fin-integrated tube performed using a cored bar as a third embodimentof the invention; and

FIG. 19 is a perspective view of a conventional fin-integrated tube.

PREFERRED EMBODIMENTS OF THE INVENTION First Embodiment

FIG. 1 is a general view of a manufacturing apparatus according to afirst embodiment of the invention, which manufactures a fin-integratedtube 2 shown in FIG. 2. The fin-integrated tube 2 is used for variousvehicle-mounted heat exchangers. The fin-integrated tube 2 is made froma cylindrical tube material 2′. The tube material 2′ is plastic-deformedby a rolling roller head 4 of a form rolling part 6 to form thefin-integrated tube 2 including a tube 21 and a fin 22 wound spirally onthe outer periphery of the tube 21 at a predetermined pitch. FIG. 3 is apartially enlarged view of the form rolling part 6 which is a main partof the manufacturing apparatus. FIG. 4 is plan and side views of therolling roller head 4 of the form rolling part 6.

FIG. 5 is a partially enlarged view of an exhaust heat recovery deviceincluding the fin-integrated tubes 2. FIG. 6 is a cross-sectional viewof the exhaust heat recovery device. FIG. 7 is a perspective view of theexhaust heat recovery device. The heat recovery device is for recoveringexhaust heat emitted from an engine, and exchanging heat with enginecooling water. The exhaust heat recovery device is used for warming theengine to increase fuel economy. As shown in FIGS. 6 and 7, the exhaustheat recovery device includes a heating section (heat exchangingsection) 1 housing a plurality of the fin-integrated tubes 2, a heatguard 100 above which a tank is disposed, and a condensing section 101having a LCC pipe P through which the engine cooling water (LLC) flows.The heating section 1 is mounted inside a duct D provided midway of theexhaust passage of the engine. The condensing section 101 is disposed inthe upper space of the tank. The heating section 1 and the condensingsection 101 are loop-connected to each other through a steam passage 102and a valve 103 to constitute a loop heat pipe (heat loop) enclosingworking medium. The loop heat pipe operates to transfer heat byevaporation and condensation of the working medium. In this embodiment,pure water is used as the working medium.

The heating section 1 includes a plurality of the fin-integrated tubes 2which are arranged in rows along the flow direction of the exhaust gasand in rows along the direction perpendicular to the flow direction ofthe exhaust gas within the duct D. Each of the fin-integrated tubes 2includes the tube 21 extending in the direction perpendicular to theflow direction of the exhaust gas and the spiral fin 22 projectingradially outward from the periphery of the tube 21. The bottom end ofthe tube 21 is closed, and the top end of the tube 21 penetrates througha core plate 3 forming the bottom plate of the tank and opens to thelower space in the tank. The inside of the tank is partitioned into theupper space and the lower space by a tank inner 4. The tank inner 4 isformed with the steam passage 102 projecting upward. The lower space towhich the fin-integrated tubes 2 open and the upper space in which thecondensing section 101 is disposed are in communication through thesteam passage 102.

The steam introduced from the steam passage 102 into the condensingsection 101 exchanges heat with the engine cooling water by contactingwith the LLC pipe, and becomes condensed water. The condensed water isrefluxed back to the heating section 1 by opening or closing the valve103 depending on the pressure inside the tank. A partition 105 having anoxygen introducing hole 104 is provided in the lateral direction of thesteam passage 102 for removing oxygen generated by contact betweenhigh-temperature steam and metal, for example. A copper oxide containingcase 106 containing granular copper oxide 107 is provided below thespace partitioned by the partition 105. The generated hydrogen is guidedfrom the hydrogen introducing hole 104 to the copper oxide containingcase 106, and reduced to be removed.

As shown in FIG. 5, the fin 22 is integrally connected to the tube 21 atits proximal end portion, and exchanges heat with the exhaust gascontacting the fin surface at its thin distal end portion which isspirally joined to the tube 21 in layers at a predetermined fin pitch(Fp) in the axial direction of the tube 21. The fin-integrated tube 2 isexposed to high-temperature exhaust gas in the duct D. Accordingly, thefin-integrated tube 2 is made of a heat-resistant andoxidation-resistant metal such as stainless steel. As described in theforegoing, conventional fin-integrated tubes manufactured by brazinghave a concern that their fins may be deformed in a usage environmentwhere the temperature of exhaust gas is high (100 to 900° C., forexample) causing the heat exchange efficiency to be lowered.

Hence, in this embodiment, the tube material 2′ undergoes a specificrolling process in order to form the continuous spiral fin 22 integralwith the periphery of the tube 21. The tube material 2′ before therolling process is approximately 10 mm in outer diameter, approximately7 mm in inner diameter, and approximately 1.5 mm in wall thickness. Thefin height (Fh) and the fin thickness (Ft) are determined so as toachieve a target heat exchange performance and a target exhaust flowperformance (exhaust flow pressure loss). The wall thickness of a partof the peripheral portion of the tube material 2′, which is used as afin forming portion, is set smaller than the thickness (t) of the tube21 (or smaller than a half of the wall thickness of the tube material2′), for example, approximately 0.7 mm, to provide a thin and high finshape. For example, when the fin pitch is 1.5 mm, the fin formingportion is plastic-deformed in the radial direction such that the finheight is between 1.8 mm and 2.6 mm to achieve the target performances.

Generally, a common rolling process is for plastic-deforming a rowmaterial to the shape analogous to the shape of the outer surface of arolling roller by pressing the rolling roller to the periphery of therow material. Accordingly, common rolling rollers are not suitable forshaping the thin-wall tube material 2′ to have a thin-wall fin bydeforming the tube material 2′ to expand radially outward. Hence, anewly developed rolling roller head 4 specialized for use in fin formingis used in this embodiment. A manufacturing apparatus including therolling roller head 4, and a method of manufacturing the fin-integratedtube using this manufacturing apparatus are explained in the following.

As shown in FIG. 1, the manufacturing apparatus for manufacturing thefin-integrated tube 2 has a processing bench 7 on which a tube holdingpart 3 for holding and fixing the tube material 2′ to be processed andthe for rolling part 6 including a rolling roller head 4 of three-rollertype and a rolling head holder 5 are mounted so as to be opposed to eachother. The tube holding part 3 includes a holding chuck 31 for holdingthe proximal end portion (the left end portion in FIG. 3) of thematerial tube 2′. The holding chuck 31 is mounted to a rotating shaft 32coupled to a driving part 72. The tube material 2′ can be rotated byrotating the rotating shaft 32. The form rolling part 6 is axiallymovable on the processing bench 7 by a conveying shaft 61 mounted on asupporting table 62 supporting the rolling head holder 5 to which theroller head 4 is mounted. The driving part 71 drives the conveying shaft61 in synchronism with the rotating shaft 32 to move the rolling rollerhead 4 toward the end portion (the right end portion in FIG. 1) of thetube material 2′ disposed coaxially with the rolling roller head 4 at apredetermined speed.

As shown in FIG. 3, the rolling roller head 4 includes a flange portion44 to which the roller group (the rollers 41, 42 and 43) is mounted anda cylindrical proximal end portion 45. The cylindrical proximal endportion 45 of the rolling roller head 4 is inserted and fixed to amovable sleeve 52 having a container-like shape. The movable sleeve 52is axially and slidably supported in a slide hole 51 formed so as toopen to one end (the left side end in FIG. 3) of the head holder 5. Therolling head holder 5 includes an axially elongated hole 55 penetratingthrough the lateral wall of the slide hole 51. The movable sleeve 52includes locking pins 54 formed in the periphery thereof so as toproject from the elongated hole 55 to restrict the movable sleeve 52from moving in the rotating direction. Between the bottom of the movablesleeve 52 and the other end (the right side end in FIG. 3) of therolling head holder 5, a coil-shaped compression spring 56 is disposedas a biasing member to bias the movable sleeve 52 toward the rollingroller head 4.

The movable sleeve 52 and the spring 56 constitute an extensionabsorbing mechanism for absorbing extension of the tube material 2′being form-rolled. The movable sleeve 52 can move to a distanceadaptable to extension of the tube material 2′. The spring 56 isdisposed in the rear of the movable sleeve 52 (opposite the rollingroller head 4) and always biased forward (toward the tube formingdirection) at an appropriate load. The biasing force applied to themovable sleeve 52 can be determined through pretest to such a value thatgenerates a pressing force enabling the roller crests of the rollingrollers 41, 42 and 43 to bite the periphery of the tube material 2′ atthe beginning of a forming process and to retract to absorb extension ofthe tube material 2′. An adjustment screw 57 is mounted to the openingformed in the other end (the right side end in FIG. 3) of the rollinghead holder 5. By screwing in the adjustment screw 57 in the axialdirection, the compression amount of the spring 56 to which theadjustment screw 57 abuts can be adjusted.

As shown in FIG. 4, the rolling roller head 4 includes, as a rollingroller group surrounding the periphery of the tube material 2′ in threedirections, the three rolling rollers 41, 42 and 43 disposed in aconcentric pattern at even intervals. Each of the rolling rollers 41, 42and 43 includes a plurality of the roller crests 44 at its periphery toform a desired fin shape. The rolling rollers 41, 42 and 43 arerotatably supported by the rolling roller head 4 such that they areinclined by a predetermined lead angle (three degrees in thisembodiment) to the center axis of the tube material 2′.

As shown in FIG. 8, the roller crests 44 are formed of concavo-convexportions arranged in the axial direction at even pitch. The threerolling rollers 41, 42 and 43 are displaced by a predetermined pitchfrom one another in the axial direction. Accordingly, by sending therolling roller head 4 in synchronism with rotation of the tube material2′ (one pitch per one rotation), the tube material 2′ is pushed inbetween the rolling rollers 41, 42 and 43, and the rolling rollers 41,42 and 43 move relative to the tube material 2′ in the axial directionwhile being driven to rotate. As a result, the roller crests 44 of therolling rollers 41, 42 and 43 move past the periphery of the tubematerial 2′ in succession while pressing the periphery to form the fin22 projecting spirally.

It is not easy to form such a fin shape which is thin and has a largeheat transfer area. Hence, this embodiment uses the three rollingrollers 41, 42 and 43 as a gradual roller whose roller crests 44 changein shape stepwise along the axial direction. More specifically, as shownin FIG. 9, the end portions of the roller crests 44 of each of therolling rollers 41, 42 and 43 are rounded so as to be R-shaped portionshaving a circular arch shape (referred to as the “R-shaped end portions”hereinafter), the sizes (widths) of the R-shaped end portions becominggradually larger from one axial end to the other axial end. The rollercrest 44 at the one axial end has a roughly triangular-cross section asa whole and is formed to a shape of sufficiently small “R” at its end,so that it can bite the tube material 2′ easily. The arc diameters ofthe R-shaped end portions are gradually increased along the axialdirection, and accordingly, the roller crests 44 near the other axialend (near the rolling head holder 5) have an inverted U-shapedcross-section as a whole.

The tube material 2′ is not deformed easily because the rolling rollerhead 4 applies load in three directions. In addition, since the threerolling rollers 41, 42 and 43 serve as a gradual roller, the processingload can be reduced. The roller crests 44 of the rolling roller groupconstituted of the three rolling rollers 41, 42 and 43 are shaped suchthat the R-shaped end portions become gradually larger in the time orderof abutment on the tube material 2′. Some of the adjacent R-shaped endportions may be the same in shape, if the arc diameters (R) of theR-shaped end portions of the roller crests 44 increase stepwise in theaxial direction as a whole.

Preferably, the R-shaped end portions of the roller crests 44 of therolling rollers 41, 42 and 43 are different from one another in shapeexcept those at their both ends. FIG. 9 shows an example of this case,where each of the rolling rollers 41, 42 and 43 includes 13 rows of theroller crests 44 arranged along the axial direction, the arc diameter Rat the 1st row being a mm (R=a) for all of the rolling rollers 41, 42and 43, the arc diameters R at the 12nd and 13rd rows being 6a mm (R=6a)for all of the rolling rollers 41, 42 and 43. In this example, the arcdiameter R at the 2nd row is a mm for the rolling roller 41, a+0.02 mmfor the rolling roller 42, and a+0.04 mm for the rolling roller 43. Forthe 3rd to 10th rows, the arc diameter R is increased with the increaseof the row number for all of the rolling rollers 41, 42 and 43. The arcdiameter R at the 11th row is 6a-0.05 mm for the rolling roller 41,6a-0.03 mm for the rolling roller 42, and 6a-0.01 mm for the rollingroller 43. It is possible to disperse the processing load to therebyform the fin shape with high precision by differentiating the rollercrests 44 in shape, and to reduce variation of the formed fin shape byequating the shapes of the roller crests 44 of the rolling rollers 41,42 and 43 at the beginning and end of the fin forming process.

FIGS. 10 and 11 are schematic diagrams for explaining the fin shapingprocess using the rolling rollers 41, 42 and 43 as a graduallyR-changing roller. At the beginning of the tube forming process, the finforming portion of thickness of t of the periphery of the tube material2′ is pushed into the shape analogous to the roller crests 44 at a smallload. Thereafter, the R-shaped end portions of the roller crests 44pushing into the periphery of the tube material 2′ are graduallyincreased in size, as a result of which the tube material 2′ is squeezedbetween the lateral sides of the roller crests 44 to be plastic-deformedso as to extend upward. Accordingly, since the pushing force isdispersed to the lateral sides, the fin shaping process can be smoothlyperformed by squeezing up the fin forming portion so as to change from aroughly trapezoidal shape to a desired fin shape using the rollercrests.

As shown in FIG. 10, the root portions between adjacent roller crestsare shaped such that they become gradually deeper in the direction fromthe end at which the R-shaped end portion is minimum to the end at whichthe R-shaped end portion is maximum. As shown in FIG. 11, the fin heightis gradually increased. Accordingly, the depth of the root portion atthe end at which the R-shaped end portion is minimum can be madesufficiently small to prevent the rolling rollers 41, 42 and 43 frombeing broken, because it is only required to hold the fin 22 at thisend. The root portions are shaped such that their depths graduallyincrease with the progress of the fin shaping process so as to providenecessary spaces for holding the fin being formed to project radiallyoutward.

Next, the advantages of using the roller crests of the rolling rollers41, 42 and 43 are explained with reference to FIGS. 12 and 13. As shownin FIG. 12, the roller angle (the angle theta formed by the lateralsides of adjacent roller crests 44) is V-shaped when their R-shaped endportions are small, and becomes gradually narrower as the R-shaped endportions become larger. Accordingly, the pushing force is dispersed tothe lateral sides to facilitate the fin shaping. As shown in FIG. 13,the roller crests 44 are rounded at their ends, and the widths of theirends are gradually increased (as roller crests of a totally graduallyR-changing roller). Accordingly, it is possible to prevent a shearingstress from concentrating in their ends and to disperse the shearingstress to the lateral sides. Further, since the arc diameters (R) aregradually increased, most of the portion being shaped by the followingroller is limited in the area facing a 45-degree lateral sector of thecircumference of the leading roller. This makes it possible to extendthe fin forming portion upward by a large amount, because the formingload can be sufficiently dispersed to the lateral sides while squeezingthe thick wall portion at the fin proximal end portion.

Next, effects of the extension absorbing mechanism provided in therolling head holder 5 are explained with reference to FIGS. 14 and 15.In this embodiment, as shown in FIG. 14, extension toward the chuck 31occurs in the tube material 2′ when the leading roller crest 44 (thefirst crest in FIG. 14) of each of the rolling rollers 41, 42 and 43bites the periphery of the tube material 2′. Since this extension isaccumulated for each of the roller crests biting the periphery of thetube material 2′, the tube material 2′ is likely to be axiallycompressed and deformed. On the other hand, the rolling head holder 5shown in FIG. 15 is configured such that the proximal end portion 45 ofthe rolling roller head 4 is resiliently supported by the movable sleeve52 and the spring 56 so as to be movable relative to the rolling headholder 5. Accordingly, the rolling head holder 5 shown in FIG. 15 canrelease the tube extension stress occurring between the tube material 2′rotating pivoted at one end thereof and the rolling roller head 4advancing forward at a constant speed by receiving the tube extensionstress in the movable sleeve 52 and retracting the spring 56 whilecompressing it. Hence, according to the rolling head holder 5 shown inFIG. 15, it is possible to prevent the tube material 2′ from beingdeformed by absorbing the extension of the tube material 2′.

Second Embodiment

FIG. 16 is a side view showing an example of the shape of the rollercrests of a modification of the rolling roller head 4 included in amanufacturing apparatus according to a second embodiment of theinvention. FIG. 17 is a schematic diagram for explaining a tube formingprocess performed using the modification of the rolling roller head 4.In the second embodiment, as shown in FIG. 16, each of the rollingrollers 41, 42 and 43 is constituted of a first rolling roller 4 a and asecond rolling roller 4 b to enable performing a two-stage rolling. Thefirst rolling roller 4 a, which is a main part of the rolling rollerhead 4, is a gradually R-changing roller whose R-shaped end portions ofthe roller crests 44 become larger gradually as is the case of the firstembodiment. That is, as shown in FIG. 17, the R-shaped end portions aresmaller at the forward end of the tube material 2′ and larger at therearward end of the tube material 2′ so that the fin forming portion issqueezed radially outward (upward in FIG. 17) gradually (Ft1). In thefirst rolling roller 4 a, the heights (outer diameters D1) of the rollercrests 44 are the same, while the depths of the root portions betweenadjacent roller crests 44 become gradually larger so that the finforming portion which becomes gradually higher with the progress of thefin shaping process can be held in the root portions securely.

In FIG. 16, the second rolling roller 4 b disposed following the firstrolling roller 4 a is a projecting roller configured such that theheights (outer diameters D2) of the roller crests 44 are higher thanthose of the first rolling roller 4 a, and become gradually largertoward the rear end thereof. As shown in FIG. 17, since the tubematerial 2′ is gradually pushed radially inward (Fh2: downward in FIG.17), the fin height can be more increased. Since the tube material 2′has been made thin by the first rolling roller 4 a, the plasticdeformation by the second rolling roller 4 b can be facilitated.

Third Embodiment

Next, a third embodiment of the invention is described with reference toFIG. 18. FIG. 18 is a schematic diagram for explaining a method ofmanufacturing a fin-integrated tube performed using a cored bar as athird embodiment of the invention. As shown in FIG. 18, there is slightplastic deformation in the inner wall of the formed tube 21 in thedirection in which it was pushed by the rolling rollers 41, 42 and 43.Such plastic deformation can be reduced by performing the formingprocess using a cored bar 8 mounted to the inner wall of the tube 21.Using the cored bar 8 facilitates the roller crests 44 to bite the tube21, and minimizes escape of the tube 21 caused by resilient deformationof the tube 21 at the time of pushing the roller crests 44 into the tube21, to thereby maximize the height of the fin 22. Further, using thecored bar 8 reinforces the thin tube 21 and makes it resistant tobending.

The fin-integrated tube 2 of the invention underwent a heat endurancetest in a state of being mounted to the exhaust heat recovery deviceshown in FIGS. 6 and 7. More specifically, the exhaust heat recoverydevice was fabricated by disposing a plurality of the fin-integratedtubes 2 inside the duct D to constitute the heating section 1, and thetemperature of the gas flowing into the duct D was changed repeatedly(2,000 cycles) within the range from 100 to 900° C. For comparison, thesame test was performed for the conventional fin-integrated tube shownin FIG. 19.

It was found that the fin 22 of the fin-integrated tube 2 of theinvention did not change in shape before and after the test. Further,the heat exchange performance and the pressure loss were found to bewithin a predetermined standard. On the other hand, in the case of theconventional fin-integrated tube, the fin deformation graduallyincreased with the increase of the cycles due to difference in linearexpansion coefficient in the dissimilar metal joint thereof. After 2,000cycles of the change of the gas temperature, the heat exchangeperformance dropped by 25%, and the pressure loss dropped by 50%. Fromthis test, it was confirmed that the fin-integrated tube 2 of thepresent invention exhibits high durability under high temperatureenvironment.

The manufacturing method of the present invention enables manufacturingfin-integrated tubes integrally provided with a spiral fin with a highdegree of formability by using the three-roller type rolling roller headincluding gradual rollers. According to the manufacturing method of thepresent invention, since the tube material 2′ is plastic-deformed, thematerial is not wasted unlike in conventional machining or cutting work,and it is easy to adjust the heat transfer area (heat exchangeperformance) of the fin by adjusting the fin pitch depending on the leadangle of the rolling roller.

In the above embodiments, stainless steel is used as the material of thefin-integrated tube 2. However, a metal material having good heatconductivity such as aluminum or copper, or an alloy of them may be useddepending on the usage environment. The material of the rolling rollers41, 42 and 43 can be determined depending on the material of the tubematerial 2′. For example, when the tube material 2′ is made of a hardmaterial, the rolling rollers 41, 42 and 43 may be made of a strongermaterial such as an ultrahard alloy.

The fin-integrated tube manufactured by the manufacturing method orapparatus of the present invention can be used for various heatexchangers other than exhaust heat recover devices, such as those usedin a cooling system, a driving system or an air-conditioning system of avehicle.

The above explained preferred embodiments are exemplary of the inventionof the present application which is described solely by the claimsappended below. It should be understood that modifications of thepreferred embodiments may be made as would occur to one of skill in theart.

What is claimed is:
 1. A method of manufacturing a fin-integrated tubefor a heat exchanger, the fin-integrated tube including a cylindricaltube and a spiral fin integrally formed in a periphery of the tube,comprising the steps of: disposing a rolling roller group including aplurality of rolling rollers each having a plurality of roller crests ona periphery thereof so as to surround the periphery of the tube with apredetermined lead angle, each of the roller crests being rounded at anend thereof into an R-shape to be an R-shaped end, widths of theR-shaped ends of the roller crests being gradually increased from oneaxial end to the other axial end for each of the rolling rollers, sothat each of the rolling rollers serves as a gradual roller; and causingthe roller crests of the rolling rollers to press the periphery of thetube from the one axial end to the other axial end by axially moving androtating the rolling roller group relative to the tube so as to deform apart of the periphery of the tube into a spirally projecting portionwhile shaping the spirally projecting portion into the spiral fin bygradually squeezing the part of the periphery of the tube using theR-shaped end portions of the roller crests of the rolling rollers. 2.The method of manufacturing a fin-integrated tube for a heat exchangeraccording to claim 1, wherein the fin-integrated tube is made ofstainless steel.
 3. A manufacturing apparatus for manufacturing afin-integrated tube for a heat exchanger, the fin-integrated tubeincluding a cylindrical tube and a spiral fin integrally formed in aperiphery of the tube, comprising: a tube holding part for holding aproximal end portion of the tube so as to be rotatable together with thetube; and a rolling roller head disposed coaxially with the tube so asto be axially movable relative to the tube; the rolling roller headhaving a rolling roller group including a plurality of rolling rollerseach having a plurality of roller crests on a periphery thereof, saidrolling roller group being configured to surround the periphery of thetube with a predetermined lead angle, each of the roller crests beingrounded at an end thereof into an R-shape to be an R-shaped end, widthsof the R-shaped ends of the roller crests being gradually increased fromone axial end to the other axial end for each of the rolling rollers, sothat each of the rolling rollers serves as a gradual roller, wherein therolling roller head is configured to be driven to axially move in adirection from a distal end to a proximal end of the tube and rotaterelative to the tube so as to cause the roller crests of the rollingrollers to press the periphery of the tube in the direction from thedistal end to the proximal end so as to deform a part of the peripheryof the tube into a spirally projecting portion while shaping thespirally projecting portion into the spiral fin by gradually squeezingthe part of the periphery of the tube using the R-shaped end portions ofthe roller crests of the rolling rollers.
 4. The manufacturing apparatusfor manufacturing a fin-integrated tube for a heat exchanger accordingto claim 3, wherein heights of the roller crests of each of the rollingrollers increase stepwise in a direction from one axial end to the otheraxial end thereof.
 5. The manufacturing apparatus for manufacturing afin-integrated tube for a heat exchanger according to claim 3, furthercomprising: a rolling head holder holding the rolling roller head suchthat the rolling roller head is opposed to the tube holding part on aprocessing bench, the rolling head holder being formed with a slide holewhich opens to an end thereof facing the tube holding part; a movablesleeve slidably held inside the slide hole and supporting a periphery ofa proximal end portion of the rolling roller head; and a biasing meansfor biasing the movable sleeve in a direction in which the rollingroller head advances; the slide hole, the movable sleeve and the biasingmeans serving as an extension absorbing mechanism for absorbingextension of the tube being form-processed by the manufacturingapparatus.
 6. The manufacturing apparatus for manufacturing afin-integrated tube for a heat exchanger according to claim 3, whereinthe fin-integrated tube is made of stainless steel.